1. Field of the Invention
This invention relates to erosion control devices for shorelines.
2. Prior Art
Erosion of shorelines as a consequence of wave action is a well recognized phenomenon. The prior art is replete with numerous attempts and various structures to minimize this problem. Generally, erosion is a function of a persistent wave action exerted on beaches comprised of sand or fine shingled material and is most frequently encountered along shorelines of large bodies where such action can be generated. As a consequence of this persistnet wave action, material on the shore tends to be loosened by the wave action and the continuous reciprocating movement along that shoreline causes such materials to generally erode away. The problems of erosion are well known and are emphasized in situations of exceptionally long shorelines where the phenomena of littoral drift is enhanced. In those situations, breakwaters and the like only tend to emphasize downstream erosion problems.
In view of the fact that the dynamics of the problem are well understood and that erosion is a commonplace occurrence, the prior art has been highly developed in this area. Despite that development, various problems exist in these devices which have generally resulted in no one proposal being widely accepted. Accordingly, erosion control is the subject of continuing research.
One class of prior art devices attempts to deal with the problem by means of massive bulwarks or other large structures. These devices are very cumbersome, expensive and difficult to install.
To overcome the problems of installation and general size, various prior art attempts have been made to modularize components. One such attempt is shown in U.S. Pat. No. 3,875,750 wherein a modular device having a series of peaks and depressions is shown to break up various wave action phenomena. The return paths 44 and 46 shown in FIG. 2 of that patent allow water from the dissipated wave to return back to the body. Various arrangements of these components are utilized to build up a continuous breakwater for dissipation of waves. Also, as a consequence of the use of a return path for water, sand and loose material carried by the waves is allowed to build up behind the barricade, thereby building up the shoreline on the land side of the sea wall. One difficulty with the device shown in this prior art patent is that its orientation is critical vis-a-vis the wave action, and in the case of extraordinary waves, if the device is tipped over on its side, it will be rendered inoperative. Also, the costs of construction might be high in view of the intricate patterns involved.
To overcome the cost problem, U.S. Pat. No. 3,894,397 defines an erosion device utilizing ordinary concrete blocks having courses interlocked between them. As in the case of other prior art devices, extraordinarily large wave action may disorient or tip such a device thereby rendering it inoperative and leading to its early destruction by wave action. Another problem tending to increase the cost of such a device is the fact that because ordinary concrete building blocks are utilized, the path for water is exceptionally large and the dissipation of kinetic energy in the wave is relative inefficient. Therefore, additional elements in the form of flappers 30 shown in FIGS. 5 and 6 are required to dissipate wave action to a greater extent than that attained solely by the concrete block pattern and also to facilitate the removal of entrained materials in the waves themselves. Bonding techniques are weak, and blocks become loose.
Other types of prior art erosion devices are typified by mechanical structures which are erected and anchored in the shoreline to interrupt and disperse wave action by means of a series of baffles. U.S. Pat. Nos. 3,309,876 and 3,845,630 typify this class or prior art devices. Such devices, which require anchoring to the seabed, are expensive and difficult to maintain. Additionally, while located below the low means water level at the particular area of installation, such devices, nevertheless, present a menace to navigation since they are generally unmarked and unknown to mariners.
A third class of devices is typified by U.S. Pat. No. 3,952,521 and relate to portable erosion control devices. As is readily apparent, the device as typified by that patent is large, complicated in shape, and generally expensive. While the advantage of mobility ensues with those devices, their general expense and unmanageability have condemned attempts in that direction.